Most bicycles of today are of a sit-up diamond frame design. Numerous attempts have been made to introduce recumbent bicycle designs, with limited success, despite their potential advantages in comfort and ergonomically superior power utilization potential. While resistance to change has been one reason for limited success, another has been the difficulty working around the geometric limitations of the recumbent design itself, to design a bicycle that is practical, stable, safe, maneuverable, and easy to ride. There have been two general classes of solutions in the more common and comfortable feet forward position. One is the long wheel base solution, characterized by Jarvis' U.S. Pat. No. 690,733 of Jan. 7, 1902. The second is the short wheel base solution characterized by Fried, U.S. Pat. No. 2,482,472), Turner et. al (U.S. Pat. No. 4,333,664), and McElfresh, (U.S. Pat. No. 4,618,160).
Both of these general designs have been built with hand operated steering means (usually handlebars) below the rider's legs or above the rider's legs. While designs with steering means below the riders legs have come on the market, they have had limited market acceptance. It is the belief of the present inventor that riders feel safer with handlebars in front of them, especially in emergency situations.
A major design problem in the manufacture of recumbent bicycles has been that the positions of the basic components of the bicycle (wheels, seat, steering axis means, hand operated steering means, and foot operated power input means) need to be fitted to the individual rider. In diamond frame conventional bikes, the only components that are adjustable are the seat, and to a limited extent, the handlebars. Otherwise, one frame size fits a fairly wide variety of riders. A child who starts out on a conventional 20 or 24 inch wheel bike, can graduate directly to a 26 inch or 700 mm wheel adult bike of present manufacture. Only in expensive conventional bikes is frame size considered at all significant. Because of design constraints, a change of 1 or 2 inches in leg length can make a non-adjustable recumbent bicycle not fit its rider.
It is especially difficult to fit the short wheel base recumbents to different sized riders, and different riding conditions. The short wheelbase design is potentially much more maneuverable and easier to store than the long wheelbase configuration because of its smaller size. However its design is more complex and constrained. Its major components are especially constrained in their positions in order that they stay out of the way of each other and the rider while at the same time being configured to provide good rideability. Optimization of the interrelationships between these components has never been thoroughly researched because a thoroughly adjustable frame, allowing adjustment between all components, or each one with respect to all the rest heretofore never been provided.
In the adjustable frame semi-recumbent design of Buckler, (U.S. Pat. No. 4,925,203), the seat is adjustable with respect to the rest of the frame. However frame construction is such that seat position is taken as a variable, rather than a possible given, around which to adjust the rest of the frame. Adjustments of the seat relative to the rear wheel, its axle, and its ground contact patch, which patch lies directly below the axle, change the fore and aft weight balance of the machine, and therefore effect handling and riding quality.
In the present invention, the position of the seat can be set so that it just clears the rear wheel as it is moved upwardly and back, or forward and down. Its position with respect to the rear wheel can therefore be optimized according to use, and the positions of the remaining components adjusted to fit the rider. This makes it possible to minimize the length of the forward extension to the pedal assembly, and the total length of the bicycle, as well as to optimized geometry for rideability. While Buckler has rudimentary means to alter wheelbase and steering axis angle (by replacing parts) he does not provide any independent adjustment in pedal crank assembly position. Adjustments for rider leg length are made in the elements connecting the seat to the main frame member, moving the seat with respect to the rest of the frame. This is the only infinitely variable adjustment on the Buckler machine.
In addition, the Buckler bicycle is a semi-recumbent, not a true recumbent, as is the machine described herein. As such it is not designed so that the pressure created by pushing on the pedals is directly transferred to the seat back, as is the case on a true recumbent, such as the present design. With the Buckler machine, pedal pressure is counteracted by gravity and upward tension on the steering handlebars.
The recumbent frames of McElfresh (U.S. Pat. No. 4,618,160), Turner et al. (U.S. Pat. No. 4,333,664), and Fried (U.S. Pat. No. 2,482,472), all embody non-adjustable frame structures between the foot operated pedals and the rear wheel. Any adjustment for operator leg length on these designs compromises the position of the rider's center of gravity with respect to the rear wheel, a critical parameter in terms of rideability. Turner et al. and Fried provide no adjustments other than seat position. McElfresh provides means to adjust the distance between the seat and the front wheel steering axis, but he does not provide for, or teach in his specification, adjustment of the steering axis angle. This angle in fact changes as the front wheel assembly is moved along the frame in his design. In addition, all of his drawings show the imaginary upward extension of the steering axis to be well ahead of the rider's body and head, a poor choice for another very important design parameter that will be discussed in greater depth later.
The prior art recumbents that most resemble the present invention are unpatented. They include the ATP, the Presto, and the Lightning. These bicycles are provided with what is termed in the industry an adjustable boom, a single telescopic member that corresponds to the triangulated front extension of the present invention. While this configuration allows the frame to be adjusted to riders of differing leg length, it suffers from two limitations. First, the single member lacks the stiffness that is inherent in the triangulated structure of the present invention. Bicycles built in this way are notorious for their flexibility, an ergonometric deficiency, as well as a possible safety hazard. The earlier patents of Fried and Turner, et. al. for non-adjustable frames are specifically aimed at dealing with this deficiency. Secondly, prior art single adjustable boom bicycles lack the potential for vertical as well as horizontal adjustment of the foot power input means.
Recumbent bicycle seats are more complex than those of standard bicycles, because the seat has more than one function. On a standard diamond frame bike, the only function of the seat is to support the weight of the rider. On a recumbent there are two additional functions., The first is to support the back of the rider, and the second is to counteract the force of the rider's feet pressing on the pedals, which force is counteracted by pressure of the rider's hips against the lower seat back.
On a recumbent bicycle the hips must be supported from behind by means equal in strength to the toggle force produced by the straightening of the operator's legs against the pedals, which can be quite great. This force includes a well known torsional moment, caused by the fact that the pedals and the individual hips of the rider are off the centerline of the frame. This force is discussed by Fried and Turner et.al.